Plant and animal fat are frequently converted into fatty alkyl esters on an industrial scale where the fatty alkyl esters may serve any number of purposes including use as biodiesel. Most vegetable oils and animal fats are predominantly triacylglycerols (TAGs) also known as triglyceride. Although TAGs may be incorporated into diesel fuels without chemical modification, these compounds increase fuel viscosity, are poorly combusted and tend to prematurely foul upper cylinder engine parts. Therefore, chemical processes for converting fats and oils to alkyl esters of monohydric alcohols are now in common use to produce a fuel with lower viscosity that may be used as a direct replacement for diesel fuel. The core synthetic process of most biodiesel production technologies is transesterification (Ma F. and Hanna M. A. Bioresource technology 1999, 70, 1-15). In this process animal fat or vegetable oil consisting mostly of acylglycerols is reacted with a catalyst and alcohol. The products from the reaction are: (1) an alcohol ester of fatty acids (i.e. fatty alkyl esters); (2) co-product alcohol, such as glycerin; (3) unreacted excess aliphatic alcohol; and (4) residual and spent catalyst. The catalyst used in the synthesis of biodiesel is usually potassium or sodium hydroxide. The co-product, glycerin, is not soluble in the fatty alkyl ester. Consequently, upon the completion of the reaction the product separates into two phases, the upper alkyl ester which may contain some alkali soap and the lower glycerin layer, which contains substantial quantities of dissolved basic catalyst and may contain some alkali soap. Scheme 1 shows the transesterification of a triglyceride with three moles of alcohol in the presence of a basic catalyst releasing one mole of glycerin and three moles of fatty alkyl ester (biodiesel).

Glycerin, also known as glycerine and glycerol, is the chemical compound 1,2,3-propanetriol. It is a colorless, odorless, hygroscopic, water-soluble viscous liquid. Glycerin is used in soap, cosmetics, creams, foods, and a variety of other uses and is, therefore, a potentially valuable product. However, the glycerin produced in the reaction shown in Scheme 1 must be separated from the basic catalyst before it can be used for these applications. It is common in glycerin recovery procedures to neutralize the basic catalyst with acid to produce a salt solution, and then to distill the neutralized product. This process produces a high quality and high value 99% glycerin solution.
Lithium soap, otherwise known to those skilled in the art as lithium grease, functions as a water resistant lubricant. Lithium grease is useful as a finished product for lubrication or may be formulated into various lithium grease containing lubricant products. Lithium grease is also useful in cosmetic preparations.
In general there is a need for biodiesel manufacturing processes which produce one or more desired products while minimizing the production of waste. In particular there is a need for a method of producing biodiesel that allows for simplified recovery of desalted glycerin.